Plastic alloy which sets at room temperature



Patented F eb. 12, 1952 John P..Lyle', Jr., New Kensington, P ag assiglnor v I to Aluminum Gpmpany ofAmerica Pittsburgh,

2a., acorporation .of Pennsylvania No Drawing. Application February..16, 1951,

Serial No. 211,430

1 This invention relates to analloy composition which is plasticslightly above room temperature when first prepared but which.hardensupon standing. These .and other propertiesmake the alloy suitablefor forming molded products, especially compacted fillings used intoothrestorations.

Mercury containing metallic compositions, known as amalgams, have beencommonly employed heretofore wheremolda'b-ility at room temperature andsubsequent hardening of the molded mass have been required. They havefound special application in the filling of tooth cavities because ofthe hardness they attain and the tight fit which it is possible toachieve by packing the plastic body into a cavity and by the expansionwhich occurs during setting. However, the amalgams do not wet the toothor form a bond therewith and consequently some sepa-.

ration may occur in time.

The amalgams are usually prepared by triturating together predeterminedproportions of mercury and a solid metal or alloy in finely dividedcondition. Generally, more mercury is used than is required to form thefinal hardened body in order to insure a rapid and thorough mixing ofthe components and supply all the mercury that may be needed. Before theamalgam is molded or pressed into the desired shape, it is thereforenecessary to squeeze out or express the excess mercury. The operation istime-consuming and wasteful.

Although dental amalgams have been extensively used, they are still opento the additional weight of nickel, 25 to 45% gallium and 0.5 to

7.5% silicon. Other elements may be present as impurities or intentionaladditions if they do not substantially alter the characteristics of thealloy. The product formed from this alloy is non-toxic, attains aBrinell hardness of 80- to 150 upon standing 48 hours at roomtemperature after preparation and compaction, and it also hardens withsufficient rapidity to be useful in filling tooth cavities. Theforegoing hardness values refer to those obtained by use of a 1 s" '2.Claims. (01. 75 m) .2 diameter steel ball under a load of 1,2.61 kgs.applied for a period of 30 seconds. In addition, the'alloy formsa tightbond with a tooth and no excess gallium is required to form the plasticcomposition. A slight expansion of the alloy occurs during-setting,within the limits specified for amalgams; which is also advantageous indental work.

In mypreferred practice the ;alloy should'consistof 62 to66% by weightof nickel, -32= to-37-'% gallium and 1 to 2% silicon, which alloy willattain a Brinell hardness of to after standing 48 hours.

The nickel-silicon base may be prepared by mixing together the twometals in powder form in the proper proportions, or, the metals may bemelted to form an alloy, the alloy cast in cylindrical shape, machinedto produce chips and the chips then milled to provide the desiredparticle size. Other methods of preparing the comminuted alloy may beemployed, of course, as long as the proper particle size is obtained.

To form the gallium-containing alloy the foregoing base composition infinely divided condition is admixed with the proper proportion ofgallium. Inasmuch as gallium melts at about 30 C. (87 F.) it .is mostconvenient to warm it slightly to form a liquid and mix the liquid withthe base alloy powder. However, solid gallium may be added to the powdermixture and the temperature of the mass raised to a point when the massbecomes plastic or the gallium melts. In any case, thegallium-containing alloy should be in a plastic condition when mixed ortriturated. Once the plastic alloy is prepared there is generally nodifliculty in maintaining the desired plastic condition long enough topermit molding or filling a cavity in a tooth.

The amount of gallium required to produce the desired plasticity andpermit the attainment of a minimum Brinell hardness of 80 in thehardened product lies within the range of 25 to 45% by weight of thealloy, and preferably the proportion should be 32 to 37%. Also, withinthese limits all of the gallium is absorbed in forming the plasticmixture, consequently, there is no need for a preliminary squeezing orexpression to remove excess gallium prior to molding or compacting thealloy.

The mixing or trituration of the gallium and nickel-silicon basecomposition is preferably carried out in the conventional type of mortarand pestle apparatus employed in preparing amalgams. The period ofmixing will vary, ordinarily, between V: and 5 minutes, but should,

in any event, be long enough to produce a uniform moldable mass.

The resulting alloy appears to be drier than the usual amalgam; however,it is still sufiicient- 1y plastic to be as readily formed or compactedas an amalgam. In spite of the apparent dryness of the alloy, it has agreater wetting power than amalgams and tends to cling to a tooth orother non-metallic material against which it is pressed. As a result,there is no zone of imperfect contact between the tooth or other wettedbody and the gallium-containing filling and a firm lasting bond is thusassured.

Once the gallium-containing alloy is prepared it should be immediatelymolded or pressed into the desired shape. The compacting or condensingoperation may be conducted in the same manner as that followed inhandling the conventional dental amalgams. If the alloy has beenproperly mixed and compacted, the final rigid product will meet therequirements of the Federal Specifications for dimensional change andfiow of amalgams. The hardness, attained, however, is actually greaterthan that which usually characterizes dental amalgams. A range of 60 to63 is commonly specified for amalgams 24 hours after they have beencompacted.

It has been found that the desired results are obtained by employing acomminuted mixture of 90 to 99% by weight of nickel and 1 to 16% siliconin either elemental or prealloyed form, as mentioned above. It isimportant, in any event, that the final product be in sufficientlyfinely divided form to be readily admixed with the gallium, andto setrapid1y.a":- a

My invention may be illustrated by the following example. A mixture ofnickel and silicon powders was prepared which consisted of 63 partsnickel and 1 part silicon. The metallic mixture was then triturated with36 by weight of gallium at 35 C. for a period of 5 minutes. Theresultant alloy which had a dry appearance was packed in a mold with atool and tested according to Federal Specification U-A-45la. Thedimensional change was found to be +4.8 /cm. and the fiow percentage was2.9, both values coming with- 2. An alloy consisting of 62 to 66%nickel,'-32,

to 3'7 gallium, and l to 2% silicon.

JOHN P. LYLE, JR.

No references cited.

1. AN ALLOY COMPOSED ESSENTIALLY OF 49 TO 74% NICKEL, 25 TO 45% GALLIUMAND 0.5 TO 7.5% SILICON